There is increasing concern regarding repeated exposure of medical staff to agents which are potentially harmful to them in the long term. Such agents include anaesthetic gases.
Apparatus exists for controlled supply of anaesthetic gases to a patient. Example apparatus currently available incorporates a face mask. The mask is typically constructed to overlie the patient's face around the mouth and to form a tight seal between the mask and face. Other example apparatus includes a rigid mouthpiece on the outlet of the gas supply tube. Rather than overlying the patient's face as in the previous example, the mouthpiece is retained in the patient's mouth.
Apparatus currently available is capable of supplying gas to a patient on demand, that is only as and when required by the patient. In this respect, the apparatus often includes regulator means which incorporate a valve. In use, as a patient inhales, they apply a negative pressure to the gas supply apparatus. When this happens, a valve in the regulator is opened to permit supply of gas to the patient. In the absence of this negative pressure, the valve is closed and so prevents inadvertent release of gas other than when required by the patient. Likewise, when the patient closes their mouth or exhales, the valve is also closed to cut off the supply of gas. In this way, the gas is supplied to the patient only as and when required by them.
Such systems are particularly useful in cases where the patient is essentially in control of the mouthpiece or mask. This situation typically arises in labour or maternity wards. In those circumstances, so-called "gas and air" (a mixture of equal quantities of nitrous oxide and oxygen) is available for supply to the mother-to-be (or patient).
During labour, the patient is typically given a gas supply apparatus having a mouthpiece or mask, such as described above, and is free to draw from it as and when required. For times when the patient does not require the gas, they may remove the mask or mouthpiece from their face. When this is done, the regulator recognises that there is a lack of demand and the relevant valve is closed to shut off supply of gas to the mask or mouthpiece, as appropriate.
In this way, existing apparatus limits the extent to which anaesthetic gas is leaked into the patient's surroundings. It will be appreciated that gas leaked in this way is exposed to medical staff attending the birth. In the long term, this is likely to be detrimental to the health of the medical staff.
However, additional problems also arise in that, even though it is possible to cut off the supply to the patient, gas is nevertheless exhaled by the patient. Thus, when a patient exhales, this supplies a waste mixture of carbon dioxide and some anaesthetic gas into the surrounding atmosphere. As a result, any medical staff in attendance are also exposed to undesirable amounts of waste anaesthetic gas.
This is a particular problem in labour wards which have inadequate ventilation, which reduces likelihood of the exhaled gas being exhausted from the ward.
In the light of concern for health and safety of employees in the workplace, there is a desire to reduce the extent to which medical staff are exposed to waste anaesthetic gases. Indeed, it is expected that statutory maximum limits will be introduced. For example, a possible maximum limit could be 100 parts/million for nitrous oxide as an 8 hour time weighted average.